Unit Plan 11 (Grade 1 Math): Add/Sub within 20—Word Problems

Focus: Apply addition/subtraction strategies to real-life word problems (unknowns in all positions); use models and equations and check for reasonableness.

Grade Level: 1

Subject Area: Mathematics (Operations & Algebraic Thinking)

Total Unit Duration: 5 sessions (one week), 45–60 minutes per session

I. Introduction

Students solve one-step word problems within 20 using objects, drawings, number lines, ten frames, and equations with a symbol for the unknown. They practice all problem types—add to, take from, put together/part–part–whole (PPW), and compare—with result/change/start unknown positions. Emphasis is on making sense of the story, choosing a strategy, and checking answers.

Essential Questions

• How do I decide which operation fits a story?
• How can models and equations help me track the unknown?
• How do I check reasonableness (estimate, inverse, model) before I’m done?

II. Objectives and Standards

Learning Objectives — Students will be able to:

1. Read/retell a word problem, identify the situation (add to, take from, PPW, compare) and the unknown (result/change/start).
2. Model and solve within 20 using ten frames, PPW/number bonds, and number lines; record an equation with a symbol.
3. Solve put-together/three-addend problems with a total ≤ 20 by grouping to make 10.
4. Check solutions using estimation, inverse (addition ↔ subtraction), or a second representation.

Standards Alignment — CCSS Grade 1 (threaded across the unit)

• 1.OA.1: Use addition/subtraction within 20 to solve word problems in all positions with objects/drawings/equations.
• 1.OA.2: Solve three-addend word problems with a sum ≤ 20; use make-10 strategies.
• 1.OA.6: Add/subtract within 20 using strategies (e.g., make/bridge 10, count on/back).
• Mathematical Practices: MP.1 (Make sense & persevere), MP.4 (Model) emphasized; MP.6 threaded.

Success Criteria — Student Language

• I can tell what the story is asking and which operation I need.
• I can show a model and write an equation with a symbol for the unknown.
• I can check my answer with a second method or by using the inverse.